1. Technical Field
The present invention relates to a thermal detector, to a thermal detector device, and to an electronic instrument.
2. Related Art
In the field of thermal detectors, thermocouple type elements (thermopiles), pyroelectric elements, and bolometers are known. A thermopile uses thermocouples to directly detect a rise in temperature in a light absorbing film in association with absorption of light.
A pyroelectric element utilizes the pyroelectric effect of a ferromagnetic body to detect a temperature rise in a light absorbing film that occurs in association with absorption of light. For example, ferroelectric PZT (lead zirconate titanate), lithium tantalate, and other such crystals with a high dielectric constant give rise to changes in the level of electrical polarization when heated or cooled. Specifically, spontaneous changes in the level of polarization arise when the temperature changes, producing changes in the level of surface charge; whereas in the absence of temperature change, the surface charge is neutralized. In association with changes in polarization conditions, pyroelectric current flow is produced due to changes in the amount of surface charge between electrodes connected to both ends of the ferroelectric crystal. By detecting this pyroelectric current (polarization level or dielectric constant resulting from changes in polarization level), it is possible to sense the quantity of irradiating light (infrared or the like). Bolometers detect increases in temperature associated with light absorption by detecting changes in the resistance value of, for example, a heat-sensitive resistance element.
Additionally, infrared-ray-detecting elements, which are one type of thermal detector element, are employed in the field of small-scale elements as personal sensors, for example, and in the field of large-scale arrays as infrared camera devices, for example. While initially developed as military technologies, such elements have been introduced more frequently in consumer products of late, and various applications for infrared detection may be anticipated in the future.
Thermal type detectors are mounted, for example, on a mounting part consisting of a thin film (membrane), where the mounting part is supported in a state of being suspended above the substrate by an arm. The arm must prevent thermal diffusion to the substrate while also having mechanical strength sufficient to stably support the mounting part.
The structures of thermal photodetectors are described, for example, in Japanese Laid-Open Patent Application Publication No. 2008-3081 and Japanese Laid-Open Patent Application Publication No. 2009-229260. With the infrared sensor described in Japanese Laid-Open Patent Application Publication No. 2008-3081, a resistor that undergoes a change in resistance depending on temperature is formed on a support seating, where this support seating is supported on a substrate by a pair (two) horizontal beams of the same length. The respective horizontal beams are provided with leads (wires) that are composed of a conductor material.
With the infrared sensor element described in Japanese Laid-Open Patent Application Publication No. 2009-229260, the detection cell part is supported on the substrate by a unitary support part. The unitary support part has a shape produced by a plurality of curved parts (switch-backs) in order to reduce thermal conductance.